For example, it has been demonstrated that conductivity and surface polarity of snowman-type JPs can be tuned by changing the lobe ratio between a semiconductive lobe and an electrically insulating lobe. JPs can be multifunctional because they can carry different properties on each lobe this is especially attractive to creating new multifunctional materials where the surface and bulk-like properties can be combined to obtain unexpected functionalities. JPs can also be regarded as building blocks of matter that can self-assemble to give rise to suprastructures. Their size may also bring further advantages, for example, they can be used as carriers of actives (small molecules serving as pharmaceutically active ingredients), or smart catalysts moving in concentration gradients and even nanomotors for transportation of “heavy” cargo, which molecular surfactants cannot do. Furthermore, the JPs are also active at the air–water interface and this makes them attractive as stabilisers of air bubbles and foams. Pickering emulsions can also be generated with HPs but it has been shown that due to their amphiphilicity the JPs are several times more interfacially active and thus superior in such applications. This can be an advantage because JPs can be used as emulsifiers of oils and water and create ultrastable Pickering emulsions. First, because they are solid-state particles and due to their size, they have large interfacial attachment energies, on the order of thousands of kT (parameter that scales with the R 2, where R is the radius of the particle), meaning that once adsorbed at the interface they remain trapped and secondly their diffusion through the liquid is much slower. But unlike surfactants, generally small molecules, or low molecular weight polymers, JPs exhibit some significant differences. Due to the inherent polarity contrast between two surface regions, they resemble surfactants with one polar side and one-less polar therefore, the JPs are promising as “solid state amphiphiles” or the next generation of amphiphiles. One example of such functionality is amphiphilicity. Unlike homogeneous particles (HPs) the JPs have some interesting properties and exhibit extra-functionality conferred by their asymmetry. Probably the most typical shape of a Janus particle is that of a dumbbell or snowman, Fig. Under the same “Janus” category other particles, such as raspberry, rods or discs have also been included and generally all asymmetric particles, as long as there is a difference in composition or surface properties on the same particle but on distinctive regions. 4.1, or they can adopt different shapes, such as snowman, or dumbbell, hybridised-like orbitals, mushroom with clear geometrical and topological asymmetries. JPs can adopt different shapes, for example, perfectly spherical with two hemispheres having different surface properties as depicted in Fig. Janus particles (JPs) can be generally defined as asymmetric particles with at least two surface regions or bulk composition differing in their physicochemical properties. Interfacial activity of Janus particles.This work is intended to be a general introduction into the rapidly growing and already mature field of JPs, by giving a short historical account and an overview of the available synthetic methods as well as their application potential arising mainly through JPs ability to adsorb at air–water and oil–water interfaces. The first synthesis of micron-sized JPs was attributed to the former two authors, while de Gennes baptised them after the Roman god Janus. Janus particles have a relative recent history and came recently into existence through the work of Casagrande, Veysi and de Gennes in the late 1980s. The application potential of the JPs grew significantly in the past decade and JPs become an established platform for creating new multifunctional materials. JPs can be prepared in wide range of sizes and different bulk or surface properties can be “loaded” through selective modification on each of the Janus lobes and sometimes can be combined in surprising ways. Due to their amphiphilicity JPs become interfacially active, resembling molecular surfactants, can partition at interfaces and can emulsify and stabilise Pickering emulsions. JPs can be amphiphilic if the surface polarity contrast between the two surface regions (Janus lobes) is sufficiently large. JPs can adopt different shapes, for example, perfectly spherical with two hemispheres having different surface properties, or more commonly snowman or dumbbell shapes.
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